CONCORD — The mother and son accused of selling bogus paintings of modern artist Leon Golub still believe the 16 works sold to an international art collector are not forgeries, their lawyer said at the opening day of a trial that should last most of this week.

Lorettann Gascard, 69, the one-time director of the Franklin Pierce University art gallery, had a decades-long friendship with Golub, who gave her some of his works, her lawyer, William Pribis, told a jury in U.S. District Court. Her son, Nikolas Gascard, acquired other Golubs when his aunt, a Golub collector, committed suicide and bequeathed her estate to Nikolas, Pribis said Monday.

They still believe those works are not forgeries, Pribis said.

Pribis made his statements during the opening of a trial that will delve into the world of art collections and trading. Four pieces of the alleged forgeries — including the bare-breasted body of a woman suspended by her arms in a torture-like pose, and another of a man with a gun to his head — were on display for the jury.

A post-impressionistic painter, Golub (1922-2004) was part of the Chicago-based Monster Roster movement. Many of his works deal with inhumanity and violence.

The trial is a civil case, brought by Andrew Hall, a one-time trader in oil and commodities who now acquires painting and other art works, most from the 1960s to present day. The Hall Art Foundation exhibits them in galleries that the foundation operates in Massachusetts, Vermont and Germany. Museums and other galleries also request and exhibit pieces from his extensive collection.

Hall is alleging fraud and wants $460,000 in damages, which represent 16 paintings he purchased directly from the Gascards.

Hall’s lawyer, Ted Poretz, told the jury that Nikolas Gascard had admitted to making up the titles and creation dates for the works. And they were sold with the promise that the Gascards had obtained the paintings directly from Golub.

“He (Hall) is entitled to believe them. He’s entitled to trust them. He’s not required to go out and hire a detective anytime he wants to buy a painting,” Poretz said.

As a fraud case, Pribis said Hall’s lawyers must prove that the Gascards knew the paintings were forgeries. That’s not the case, he said.

Pribis said Lorettann Gascard met Golub at Fairleigh Dickinson University in New York in the 1960s when he was an art teacher and she a student. They struck up a friendship, he gave her about seven of his works, and they saw each other about once a year.

She married, and her husband and his sister acquired Golub works, most from the artist himself, Pribis said. In the mid-1990s, Gascard’s husband died in an accident. Eleven years later his sister, still distraught over her brother’s death, committed suicide. The Golubs ended up in Nikolas’ possession, Pribis said.

Pribis said there was never any evidence that Hall relied on the Gascards to vouch for the authenticity of the paintings.

Hall purchased the first Golub from the Gascards through Artmedia, an e-bay-like service for the art world that makes some effort to verify the authenticity of a piece. Nikolas then contacted Hall and they engaged in private sales of another 16.

Hall made no efforts to ensure the paintings were authentic, Pribis said.

A jury of two men and five women are hearing the evidence.

They won’t hear several facts: Hall’s personal finances and a lawsuit and settlement between Lorettann Gascard and Franklin Pierce University over her claims of disability, sex and age discrimination.

Judge Steven McAuliffe has ruled that lawyers can bring up Gascard art sales to other parties, the purchase price of other pieces that Hall bought from the Gascards, and an assertion that Hall had a duty to investigate the authenticity and chain of ownership of the Golub pieces in doubt.

In early testimony, Hall said he was the head of oil trading operations of British Petroleum in New York and helped the company become the world’s largest oil trader.

He ran an oil trading company that was acquired by Solomon Brothers and eventually by CitiGroup. He also ran and liquidated a commodities trading firm.

He took up art collecting around 2000 as part of a mid-life crisis, he said.

He said he purchased the Golubs from the Gascards around 2011, and only became concerned around 2015 when he planned an exhibition, and the Golub family questioned the authenticity of the work.

“(Nikolas) seemed very knowledgeable, very convincing. He was very believable. I saw no reason to doubt any of the things he was telling me,” Hall said.